The present invention generally relates to a method for forming a layer of nitrogen and silicon containing material on a substrate and more particularly, relates to a method for forming a layer of nitrogen and silicon containing material on a substrate by flowing a gas which has silicon and nitrogen atoms in the same molecule over a heated substrate at a pressure of less than 500 Torr wherein the molecules do not contain carbon.
In the recent advancement in semiconductor fabrication technologies, semiconductor devices are continuously being made smaller such that a larger number of devices can be packaged on the same chip real estate. The continuing miniaturization of devices, such as very large scale integrated (VLSI) and ultra large scale integrated (ULSI) devices, demands that each component must be reduced in dimensions. For instance, as the lateral dimensions of a semiconductor device are reduced, the thickness of each of the component layers such as an insulating layer or a conducting layer must be reduced accordingly. As the characteristic dimensions of complementary metal oxide semiconductor (CMOS) technology decrease, more stringent demands are being placed on the silicon dioxide gate insulator layer in the field effect transistor. In addition to its normal function as a circuit element in the device, the gate insulator layer must also protect the silicon substrate from possible diffusion of chemical species originating from a polysilicon gate electrode through the gate insulator/silicon substrate interface. Such chemical species include dopant atoms such as boron which can diffuse from the gate electrode through the gate insulator into the silicon substrate and thus, result in a device that no longer performs within specification. Another chemical species, hydrogen, which is normally present in the gate electrode, is also highly mobile and can react at the silicon substrate/gate insulator interface during the operation of the device. Such reaction may result in a degradation of the gate insulating layer leading to a reduced lifetime of the device. Traditionally, as long as the gate insulating layer is sufficiently thick, the layer serves to protect the substrate from the diffusive chemical species. However, with the thickness of gate insulators in modem ULSI devices shrinking to dimensions of 3 nm or less, the protection of the substrate is no longer assured. Other remedies must be provided for such devices in order to guarantee the fabrication of a transistor that operatesment.
Different ways to increase the chemical isolation provided by a thin gate insulator in a modern semiconductor device have been proposed by others. One of the methods for suppressing diffusive chemical species from the gate electrode is to introduce a very small amount of nitrogen into the silicon dioxide normally used as the gate insulator. Nitrogen acts as a barrier to a number of elemental species such as B, H, and alkali metals such as Li, Na, K, etc. Traditionally, small amounts of nitrogen can be incorporated into silicon dioxide in an uncontrolled manner, i.e., through high temperature annealing of the oxide in a nitrogen-containing gas such as NO, N2O or NH3. The high temperature required for the annealing process is normally greater than 800xc2x0 C. A nitrided oxide is thus formed which has been shown to slightly suppress boron penetration and improve hot carrier reliability.
It is known that the optimal nitrogen concentration and distribution in the oxide required to maximize both the suppression of boron penetration and the improvement of hot carrier reliability is different. For instance, to improve the hot carrier reliability, the introduction of a small amount, i.e.,  less than 2 atomic %, of nitrogen near the substrate/insulator interface is required. The amount of nitrogen at the interface cannot exceed 2 atomic %, however, without adversely affecting the device characteristics. On the other hand, the ability to suppress boron penetration is directly proportional to the total nitrogen concentration and as such, the amount of nitrogen should be as large as possible. This presents a direct conflict with the effort of improving the hot carrier reliability of the device.
Furthermore, even though the distribution of nitrogen atoms within the oxide is not important with regard to the suppression of boron diffusion, it is desirable to keep boron atoms as far away from the substrate interface as possible. By utilizing the conventional high temperature nitridation annealing process, nitrided oxides with optimal nitrogen content at the substrate/dielectric interface and maximum hot carrier reliability can be obtained. However, there are no existing methods that will also produce a high concentration of nitrogen at the electrode/dielectric interface. As a result, it is presently not possible to simultaneously optimize the hot carrier reliability and the suppression of boron penetration.
As the gate dielectric layer becomes thinner, i.e., when the oxide layer is thinner than 30 xc3x85, another undesirable effect of a large increase in electron tunneling can cause degradation of the oxide and reduced lifetime. It is therefore desirable to provide a barrier layer for blocking hydrogen from attacking the oxide layer when the oxide layer is less than approximately 30 xc3x85. The barrier layer should be advantageously positioned in between the gate dielectric and the gate electrode. The small amount of nitrogen that is incorporated into the oxide via the conventional nitridation annealing method will not act as a significant barrier to hydrogen diffusion from the gate electrode.
It is therefore an object of the present invention to provide a method for forming a layer of nitrogen and silicon containing material on a substrate that does not have the drawbacks nor shortcomings of the conventional high temperature nitridation annealing method.
It is another object of the present invention to provide a method for forming a layer of nitrogen and silicon containing material on a substrate wherein the substrate is maintained at a temperature of not less than 400xc2x0 C. to enable a pyrolysis reaction.
It is a further object of the present invention to provide a method for forming a layer of nitrogen and silicon containing material on a substrate by first heating the substrate and then flowing a gas which has silicon and nitrogen atoms in the same molecule over the surface of the substrate.
It is another object of the present invention to provide a method for depositing a layer of nitrogen and silicon containing material on a substrate wherein trisilylamine vapor [(SiH3)3N] is flowed over a heated substrate.
It is still another object of the present invention to provide a composite structure which includes a substrate and a layer of material containing nitrogen and silicon without carbon overlying the substrate for stopping chemical species from reaching the substrate.
It is yet another object of the present invention to provide a composite structure that includes a substrate, a nitrided oxide layer on the substrate and a layer of nitrogen and silicon containing material on top of the nitrided oxide layer for stopping chemical species from diffusing to said substrate.
It is still another object of the present invention to provide a semiconductor structure that includes a nitrogen-rich layer between a gate electrode and a gate insulator on a semiconducting substrate wherein the nitrogen-rich layer blocks diffusion of chemical species from the gate electrode to the gate insulator.
It is yet another object of the present invention to provide a semiconductor structure that includes a semiconducting substrate, with a gate insulator which may include a nitrided oxide layer, a nitrogen-rich layer and a gate electrode sequentially deposited or grown on the semiconducting substrate such that the diffusion of chemical species from the gate electrode to the gate insulator is inhibited.
The present invention discloses a method for forming a layer of nitrogen and silicon containing material on a substrate by flowing a gas which has silicon and nitrogen atoms in the same molecule over the surface of a heated substrate wherein the molecules do no contain carbon such that the layer of nitrogen and silicon containing material formed will stop diffusing species from reaching the substrate.
In a preferred embodiment, a method for forming a layer of nitrogen-containing material on a substrate can be carried out by the operating steps of first providing a substrate, then heating the substrate to a temperature of not less than 400xc2x0 C., and then flowing one or more gases one of which includes nitrogen-containing molecules over a surface of the substrate at a sub-atmospheric pressure. The nitrogen-containing molecules do not contain carbon. The gas can be flowed over the surface of the substrate at a pressure between about 1 m Torr and about 500 Torr, while the surface of the substrate can be maintained at a temperature between about 400xc2x0 C. and about 900xc2x0 C. The nitrogen-containing molecules pyrolize and react at the surface to form the layer of nitrogen-containing material. The process can be advantageously carried out in a chemical vapor deposition chamber, wherein the gases flowed therethrough can be selected from the group consisting of (SiH3)3N, SiH4, Si2H6, Si2H2Cl2, NH3, NO, N2O, N2H4 and O2.
In another preferred embodiment, a method for forming a layer of nitrogen and silicon containing material on a substrate can be carried out by the operating steps of first providing a substrate that is maintained at a temperature of not less than 400xc2x0 C., and then flowing a gas which has silicon and nitrogen atoms in the same molecule but with no carbon atoms in the molecule over the surface of the substrate at a pressure of not higher than 500 Torr.
The present invention is further directed to a composite structure which includes a substrate and a layer of material containing nitrogen and silicon without carbon overlying the substrate for stopping chemical species from reaching the substrate. The composite structure may further include a nitrided oxide layer that has a thickness of less than 10 nm deposited or grown between the substrate and the layer of material containing nitrogen and silicon. The layer of material containing nitrogen and silicon but not carbon may be stoichiometric nitride. The substrate in the composite structure may be selected from the group consisting of crystalline silicon, polycrystalline silicon, amorphous silicon, silicon germanium alloy, silicon dioxide or any other dielectric materials and substrates covered with a dielectric material. When the substrate is a gate insulator, the composite structure can be positioned with the layer of material containing nitrogen and silicon in intimate contact with a gate electrode layer. The composite structure may further be advantageously used in a CMOS device.
The present invention is further directed to a semiconductor structure that includes a semiconducting substrate, a gate insulator on the substrate, a nitrogen-rich layer on top of the gate insulator and a gate electrode on the nitrogen-rich layer, whereby the nitrogen-rich layer blocks diffusion of chemical species from the gate electrode to the gate insulator. The nitrogen-rich layer in the semiconductor structure may be a material containing nitrogen and silicon but not carbon. The semiconductor structure may further include a nitrided oxide layer placed between the substrate and the gate insulator. The nitrided oxide layer may have a thickness of less than 10 nm, while the nitrogen-rich layer may be a stoichiometric nitride. The nitrogen-rich layer may contain at least 20 atomic % of nitrogen and have a thickness of at least 5 xc3x85.